The invention relates generally to the organic chromophores for second order nonlinear optical (NLO) applications, compositions including such chromophores, and applications including such chromophores and compositions.
The development and uses of NLO chromophores, including polymer matrix development, waveguide fabrication, and optical device fabrication are well documented. An NLO chromophore (also known as a “push-pull” chromophore) comprises three fundamental building blocks represented by the general formula D-π-A, where D is a donor, π is a π-bridge, and A is an acceptor. In the art, a “π-bridge” is sometimes referred to as a “π-conjugated bridge,” “π-electron bridge, ” “conjugated π-electron bridge,” and the like. Examples of such bridges are described, for example, in U.S. Pat. Nos. 5,670,091, 5,679,763, 6,067,186, and 6,090,332. A “π-bridge” allows charge transfer from a donor to an acceptor in a chromophore. Exemplary acceptors are shown in FIG. 1, where, independently at each occurrence, R1 is hydrogen, a halogen except when bonded to a carbon alpha to or directly to a nitrogen, oxygen, or sulfur atom, or an alkyl, aryl, heteroalkyl, or heteroaryl group; Y is O, S or Se; and q is 0 or 1. Exemplary donors are shown in FIG. 2, where, independently at each occurrence, R1 is hydrogen, a halogen except when bonded to a carbon alpha to or directly to a nitrogen, oxygen, or sulfur atom, or an alkyl, aryl, heteroalkyl, or heteroaryl group; R2 is hydrogen or an alkyl, aryl, heteroalkyl, or heteroaryl group; Y is O, S or Se; m is 2, 3 or 4; p is 0, 1 or 2; and q is 0 or 1. Herein, a heteroalkyl group includes, but is not limited to, functional groups, halogen substituted alkyl groups, perhalogenated alkyl groups, and dendrons. What is meant by a functional group in generally understood in the art of organic chemistry, for example see Appendix B in Jerry March, “Advanced Organic Chemistry” 4th Edition, John Wiley and Sons, New York, pp 1269–1300. A “dendron” is a substituent that has regularly repeating subunits. A dendron may be further comprised of one or more heteroaryl group. A “dendrimer” is a macromolecular structure that contains a “core” surrounded by one or more dendrons. Often in the art, the terms dendron and dendrimer are used interchangeably. Dendrons and dendrimers are illustrated and discussed in Bosman et al., Chem. Rev. 1999, 99, 1665 and U.S. Pat. No. 5,041,516.
The particular D-π-A arrangement affects the ability of the molecule to achieve large second order NLO effects. Thus, the first molecular electronic hyperpolarizability (β, sometimes given as μβ, where μ is the dipole moment of the chromophore), which is a measure of this ability, can be tuned and optimized by changing the electronic properties of any one of D, π, or A, see Gorman and Marder Proc. Natl. Acad. Sci, USA 1993, 90, 11297. Molecular NLO effects, in turn, can be translated into bulk EO activity in a material by aligning molecules in one direction by applying an electric field.